You've combined things that do not Combine.

Your client has Business miles, some of which have nothing to do with Customer jobs, such as picking up shop supplies. They track and report all Business Mileage per the allowance method, then.

When customers pay us, that is Revenue. It doesn't matter if I justify it as Mileage or Hours or whatever. It's just part of Gross Revenue.

The "certain dollar amount per day" is also part of Gross Revenue.